Soluble guanylate cyclase (sGC) is the primary receptor for nitric oxide (NO) in vivo. sGC can be activated via both NO-dependent and NO-independent mechanisms. In response to this activation, sGC converts GTP into the secondary messenger cyclic GMP (cGMP). The increased level of cGMP, in turn, modulates the activity of downstream effectors including protein kinases, phosphodiesterases (PDEs), and ion channels.
In the body, NO is synthesized from arginine and oxygen by various nitric oxide synthase (NOS) enzymes and by sequential reduction of inorganic nitrate. Three distinct isoforms of NOS have been identified: inducible NOS (iNOS or NOS II) found in activated macrophage cells; constitutive neuronal NOS (nNOS or NOS I), involved in neurotransmission and long term potentiation; and constitutive endothelial NOS (eNOS or NOS III) which regulates smooth muscle relaxation and blood pressure.
Experimental and clinical evidence indicates that reduced bioavailability and/or responsiveness to endogenously produced NO contributes to the development of cardiovascular, endothelial, renal and hepatic disease, as well as erectile dysfunction. In particular, the NO signaling pathway is altered in cardiovascular diseases, including, for instance, systemic and pulmonary hypertension, heart failure, stroke, thrombosis and atherosclerosis.
Pulmonary hypertension (PH) is a disease characterized by sustained elevation of blood pressure in the pulmonary vasculature (pulmonary artery, pulmonary vein and pulmonary capillaries), which results in right heart hypertrophy, eventually leading to right heart failure and death. In PH, the bioactivity of NO and other vasodilators such as prostacyclin is reduced, whereas the production of endogenous vasoconstrictors such as endothelin is increased, resulting in excessive pulmonary vasoconstriction. sGC stimulators have been used to treat PH because they promote smooth muscle relaxation, which leads to vasodilation.
Treatment with NO-independent sGC stimulators also promoted smooth muscle relaxation in the corpus cavernosum of healthy rabbits, rats and humans, causing penile erection, indicating that sGC stimulators are useful for treating erectile dysfunction.
NO-independent, heme-dependent, sGC stimulators, such as those disclosed herein, have several important differentiating characteristics, including crucial dependency on the presence of the reduced prosthetic heme moiety for their activity, strong synergistic enzyme activation when combined with NO and stimulation of the synthesis of cGMP by direct stimulation of sGC, independent of NO. The benzylindazole compound YC-1 was the first sGC stimulator to be identified. Additional sGC stimulators with improved potency and specificity for sGC have since been developed. These compounds have been shown to produce anti-aggregatory, anti-proliferative and vasodilatory effects.
Since compounds that stimulate sGC in an NO-independent manner offer considerable advantages over other current alternative therapies, there is a need to develop novel stimulators of sGC. They would be useful in the prevention, management and treatment of disorders such as pulmonary hypertension, arterial hypertension, heart failure, atherosclerosis, inflammation, thrombosis, renal fibrosis and failure, liver cirrhosis, erectile dysfunction and other cardiovascular disorders.